JP3253616B2 - Temperature independent linear to exponential converter - Google Patents

Description

Description: BACKGROUND OF THE INVENTION The present invention relates generally to linear-to-exponential converter circuits, and more particularly, to exponentially applying an input signal applied thereto. The present invention relates to a temperature independent linear to exponential converter capable of generating a temperature independent signal of interest.

Many types of circuits use linear versus exponential circuits to generate a signal that is exponentially related to the input signal applied thereto. For example, the circuits forming part of the components of the communication system constitute one such type of circuit that advantageously utilizes such a linear versus exponential circuit. Typically, when a linear-to-exponential circuit forms part of such a communication component, the linear-to-exponential circuit is used to convert a linear-scale signal to a decibel-scale signal. Is done. (The decibel is a value related to the exponential function value.) The transmitter and the receiver are components of a communication system. The transmitter and the receiver are interconnected by a transmission channel, and an information signal is transmitted by the transmitter to the receiver over the transmission channel, and the receiver receives the transmitted information signal.

The wireless communication system comprises a communication system in which the transmission channel is formed by a radio frequency communication channel. The radio frequency communication channel is defined by the frequency range of the electromagnetic frequency spectrum. In order to transmit an information signal over a radio frequency communication channel, the information signal must be converted to a form suitable for its transmission over a radio frequency channel.

Converting an information signal into a form suitable for its transmission over a radio frequency communication channel is accomplished by a process called modulation, in which the information signal is imprinted on radio frequency electromagnetic waves. The radio frequency electromagnetic wave has a value within a frequency range of a frequency defining the radio frequency communication channel. The radio frequency electromagnetic wave on which the information signal is imprinted is usually called a "carrier signal", and the radio frequency electromagnetic wave is
Once modulated by the information signal, it is referred to as a modulated or modulated signal.

The information content of the modulated signal occupies a range of frequencies, often called the modulation spectrum. The frequency range including the modulation spectrum includes the frequency of the carrier signal. Because the modulated signal can be transmitted over free space by a radio frequency channel, the information signal can be transmitted between a transmitter and a receiver of a wireless communication system, and the transmitter and receiver of the communication system can be transmitted and received. The machine parts need not be located close to each other. As a result, wireless communication systems are widely used to provide communication between a transmitter and a remotely located receiver.

Various modulation techniques have been developed to modulate an information signal on a carrier signal to form a modulated signal, thereby enabling the information signal to be transmitted between a transmitter and a receiver in a wireless communication system. . Such modulation techniques include, for example, amplitude modulation (AM), frequency modulation (FM), phase modulation (PM), frequency shift keying modulation (FSK), phase shift keying modulation (PSK), and continuous phase modulation (CP).
M). One type of continuous phase modulation is quadrature amplitude modulation (QAM).

A receiver of a wireless communication system for receiving a modulated signal includes a circuit for detecting or reproducing an information signal modulated on a carrier signal. The circuitry of the receiver typically includes circuitry for converting the frequency of the modulated signal received by the receiver down, in addition to the circuitry required to detect the information signal. The process of detecting or reproducing an information signal from the modulated signal is called demodulation, and such a circuit for performing demodulation is called a demodulation circuit.

In some receiver configurations, a processor (referred to as a digital signal processor or DSP) is used to replace the traditional demodulation circuit.

The signal actually received by the receiver of the wireless communication system varies in amplitude as a result of reflection of the transmitted signal prior to reception by the receiver. Typically, the signal actually received by the receiver is the sum of the transmitted signals traveling along different paths forming signal paths of different path lengths. The transmission channel is often referred to as a multipath channel because the transmission channel over which the modulated signal is transmitted typically includes multiple different signal paths. Transmission of a signal over a signal path with a path length longer than the path length of the direct path results in signal delay, since the sum of the transmitted signals over the multipath channel is actually transmitted by the transmitter and timed by the receiver. This is because it is the sum of the signals received at different points.

Such signal delays result in interferences referred to as Rayleigh fading and intersymbol interference. Such interference causes signal amplitude fluctuations of the signal received by the receiver. When the communication system formed by the transmitter and receiver includes a mobile communication system transmitter and receiver (such as a cellular telephone system), when the receiver is located in a vehicle traveling at 60 MPH. , Transmitted by the transmitter and actually received by the receiver, the signal strength of the modulated signal may vary by about 20 decibels during a period of 5 milliseconds.

To overcome the effects of such fading, gain control circuits often form part of the receiver circuit and alternately amplify the received signal and limit the amplitude of the received signal.

The gain control circuit is usually in decibels / volt (decibels
per volt). Since decibels are logarithmic values, a linear to exponential conversion circuit also usually forms part of the gain control circuit of the receiver circuit.

Existing linear-to-exponential conversion circuits are available, which operate to produce an exponential output signal in response to a linear input signal applied thereto.

For example, Howard entitled "IC Op-Amp Cookbook"
Disclosed on pages 214-216 of the text of W. Sams, Copyright 1974, is an antilog generator for forming an exponential signal in response to the application of a signal. The antilog generator consists of discrete components.

Also, integrated circuit, INTERSIL part number ICL8049 discloses a similar such structure for integrated circuit formation. further,
Integrated circuit, INTERSIL part number ICL8048 discloses a log converter for performing log transformation.

Existing circuits for generating an exponential signal in response to the application of an input signal produce an exponential signal that is temperature dependent. The actual signal generated by such a circuit is thus temperature dependent, i.e., the actual exponential signal generated by such a circuit is one that has a value that varies with the temperature of the circuit. Thus, the signal generated by such existing circuits depends not only on the value of the signal supplied thereto, but also on the temperature.

Although both the antilog generator and its integrated circuit equivalent have attempted to provide temperature compensation to minimize the temperature dependence of the signal formed by the circuit, such attempts have been Temperature dependence cannot be completely negated.

The antilog generator disclosed by Sams includes a discrete thermistor. Attempts to compensate for the temperature dependence of the signal are often inadequate because the temperature of the thermistor is not necessarily equal to the temperature of the amplifier of the antilog generator.

Antilog generators located in integrated circuits attempt to compensate for the temperature dependence of the signals generated therefrom by forming the integrated circuit by a hybrid manufacturing process. Integrated circuits formed by the hybrid manufacturing process consist of at least two different types of materials. Such a process increases the cost of the material in addition to the manufacturing costs, and in any case, the temperature compensation circuit of such an integrated circuit likewise cannot completely eliminate the temperature dependence. Thus, attempts to compensate for the temperature dependence in this manner are often inappropriate.

Thus, the gain control circuit of the receiver component of a wireless communication system that uses such a traditional linear-to-exponential conversion circuit generates a signal that varies with the temperature level of the circuit. Thus, the gain control signal generated by such a gain control circuit may vary, at least in part, with temperature levels. Since such temperature dependence adversely affects the function of the gain control circuit of the receiver, gain control of the resulting received signal is subject to errors.

Therefore, what is needed is a linear to exponential conversion circuit that generates an exponential signal that is independent of temperature.

SUMMARY OF THE INVENTION Accordingly, the present invention advantageously provides a circuit for generating a temperature independent signal that is exponentially related to an input signal.

The present invention further advantageously provides a method for generating a temperature independent signal that is exponentially related to the input signal.

Further, the present invention advantageously provides a linear-to-exponential converter for a gain control circuit of a wireless receiver that generates a temperature-independent bias current that is exponentially related to the control voltage.

Further, the present invention advantageously provides a circuit for generating a signal that is logarithmically related to an input signal.

The present invention provides still other advantages and features, the details of which will become more apparent with reference to the following detailed description of the preferred embodiments.

According to the present invention, there is thus disclosed a circuit for generating a temperature independent signal that is exponentially related to an input signal. The circuit converts an input signal into a temperature dependent signal having a desired temperature dependency. An exponential multiplier amplifies the temperature dependent signal in response to the application of the temperature dependent signal. The exponential multiplier has a temperature dependence corresponding to and opposite to the temperature dependence of the temperature dependent signal, whereby the amplified signal formed is a temperature dependent exponentially related to the input signal. A signal independent of

BRIEF DESCRIPTION OF THE DRAWINGS The invention can be better understood with reference to the following drawings, in which: FIG. 1 shows the current developed at the collector electrode of a bipolar junction transistor as a function of its base-emitter voltage; FIG. 2 is a simplified block diagram of the circuit of the first preferred embodiment of the present invention, and FIG. 3 is that of FIG. FIG. 4 is a block diagram illustrating another preferred embodiment of the present invention, similar to FIG. 3, but FIG. 4 is a flow diagram illustrating the method steps of the method of the preferred embodiment of the method of the present invention; 3 is a simplified circuit diagram of the configuration of the preferred embodiment of FIG. 3, FIG. 6 is a schematic diagram showing a portion of a cellular communication system, and FIG. 7 is plotted as a function of frequency. FIG. 8 is a block diagram of a wireless transceiver having a receiver portion of which the linear versus exponential circuit of the present invention forms a part, and FIG. FIG. 10 is a block diagram illustrating another alternative and preferred embodiment of the present invention for forming a log signal that is independent and independent of temperature; FIG. 10 is still another preferred embodiment of the present invention for forming a log signal that is independent of temperature FIG. 11 is a block diagram showing an embodiment, and FIG. 11 is a simplified circuit diagram of the preferred embodiment of FIG.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring first to the graphical representation of FIG. 1, the power generated at the collector electrode of a bipolar junction transistor is plotted as a function of the potential difference between the base and emitter electrodes of the bipolar junction transistor. The collector current, I _c , scaled by the milliamps
Is plotted on the vertical axis 20 as a function of base-emitter voltage, V _BE , scaled in millivolts on the horizontal axis 24.

Plots 28, 32 and 36 show the relationship between the current at the collector current of the bipolar junction transistor and the voltage between the base-emitter electrodes of the bipolar junction transistor at three different temperatures T ₂ , T ₁ and T _{0, respectively} . Case, where T ₂ > T ₁ > T ₀ . plot
Looking at 28, 32 and 36, the current at the collector electrode of the bipolar junction transistor, I _c , is the voltage between the base and the emitter,
It can be seen that it depends not only on V _BE , but also on the temperature of the transistor. For example, at a particular base-emitter voltage, indicated by the dotted vertical line 40 in the drawing, the current at the collector electrode of the transistor depends on the temperature of the transistor. At temperatures T _2, the current I _c in the indicated base-emitter voltage is indicated by point 28A on the curve. At temperatures T _1, the power I _c in the indicated base-emitter voltage is indicated by point 32A, and at the temperature T _0, the indicated base-emitter voltage, V _BE current I _c is point in, Indicated by 36A.

Similarly, a vertically extending line indicated by a dotted line in the drawing.
For large base-emitter voltage than indicated by 44, the temperature T _2, the current I _c in the indicated base-emitter voltage is indicated by point 28B on the curve. At temperatures T _1, the current I _c in the indicated base-emitter voltage is indicated by point 32B on the curve, and at a temperature T _0, the current I _c in the indicated base-to-emitter voltage points Indicated by 36B.

Plots 28, 32 and 36 can be described mathematically by the following equations:

In this case, I _c is the current level of the current at the collector electrode of the bipolar junction transistor, I _sat is the saturation current characteristic of the bipolar junction transistor, and e is the value 2.71 (in this case, ln (e) = 1 , V _BE is the voltage level between the base and emitter electrodes of the bipolar junction transistor, q is the charge of the electron, k is the Boltzmann constant, and T is the bipolar junction transistor (scaled in absolute temperature). Temperature.

The above equations are shown mathematically, and the plots 28-36 in FIG. 1 are shown schematically, the current at the collector electrode and the base-emitter voltage of the bipolar junction transistor,
The exponential relationship of V _BE is shown. The above equations are also shown mathematically, and plots 28-36 of FIG. 1 schematically show the temperature dependence of the current at the collector electrode of the transistor with temperature.

Because of this temperature dependence, the signals generated by traditional linear versus exponential circuits require temperature compensation.

Turning now to FIG. 2, a circuit, generally designated by the reference numeral 70, of the preferred embodiment of the present invention is shown. Circuit 70 generates a temperature independent signal that is exponentially related to the input signal.

The input signal formed on line 74 is provided to a temperature compensation circuit 78. Temperature compensation circuit 78 converts the input signal provided thereto by line 74 to a temperature dependent signal having a desired temperature dependency. Referring to the above mathematical equation used to describe the current at the collector electrode, I _c , circuit 78 determines that the signal provided on line 74 has a temperature inverse to the temperature dependence of the above listed equation. Operate to introduce dependencies.

Temperature compensation circuit 78 generates a temperature dependent signal on line 82, which is coupled to an exponential multiplication circuit 86 to provide the temperature dependent signal thereto. Exponential multiplying circuit 86 includes at least one bipolar junction transistor forming an exponential amplifying circuit. As mentioned earlier, the at least one
Since the current at the collector electrode of one bipolar junction transistor is exponentially related to its base-emitter voltage, the current at the collector electrode is the signal applied to bias its base electrode (here, line 82). A signal that is exponentially amplified according to the supplied signal). The signal generated on line 90, suitably coupled to the collector electrode of the bipolar junction transistor of multiplier 86, is exponentially related to the input signal provided on line 82. The signal generated by circuit 86 on line 90 is independent of temperature because the temperature dependent signal generated on line 82 has a temperature dependency that is opposite to that of the at least one bipolar junction transistor.

Turning now to the block diagram of FIG. 3, a circuit, generally designated by the reference numeral 100, of another preferred embodiment of the present invention is shown in functional block diagram form. Circuit 70 of FIG.
Similarly, the circuit 100 generates a temperature independent signal that is exponentially related to the input signal provided thereto. More specifically, the circuit 100 of FIG. 3 receives a voltage signal forming an input signal and generates a temperature independent current signal exponentially related to the voltage level of the voltage signal forming the input signal. To work.

Referring now to the block diagram of FIG. 3, an input signal formed by the voltage signal is generated on line 104 and provided to a voltage-to-current converter circuit 108.
Voltage-to-current converter circuit 108 converts the voltage signal provided thereto by line 104 to a signal of a current that varies according to the level of the voltage of the voltage signal forming the input signal. The current signal generated by converter 108 is generated on line 114, which is connected to temperature compensation circuit 11
8 coupled to provide a current signal there. The temperature compensating circuit 118 is connected to the line 114 in the same manner as the temperature compensating circuit 78 of FIG.
Operates to introduce a desired temperature dependency to the current signal provided thereto and to generate a temperature dependent current signal on line 156.

Line 156 is coupled to exponential multiplication circuit 160. Exponential multiplying circuit 160, similar to exponential multiplying circuit 86 of FIG. 2, operates to generate a signal, here on line 170, which is exponentially combined with the signal provided thereto by line 156. Involved.

Like the exponential multiplication circuit 86 in FIG. 2, the circuit 160 in FIG.
Comprises at least one bipolar junction transistor forming an exponential amplifier circuit. The current at the collector electrode forms an exponentially amplified signal in response to a signal applied to bias the base electrode (here, the signal provided on line 156). Line 170 is suitably connected to the collector electrode of the transistor, and the current at the collector electrode of the transistor forms an output signal on line 170 that is exponentially related to the input signal provided on line 156. Temperature compensation circuit 78 and exponential multiplier circuit in FIG.
3, the temperature compensation circuit 118 and the exponential multiplier circuit 160 of FIG. It has a correlation that is opposite to the temperature dependence introduced into the current generated at the collector electrode of one bipolar junction transistor. Since the temperature dependent signal generated on line 156 has an inverse temperature dependence of the temperature dependence of the at least one bipolar junction transistor of circuit 160, the signal generated on line 170 by circuit 160 Not dependent. Because it is independent of temperature, the signal generated on line 170 does not change in response to changes in ambient temperature.

Turning now to the flow diagram of FIG. 4, for generating a temperature independent signal exponentially related to the input signal,
The steps of a method according to a preferred embodiment of the present invention are shown.

First, as indicated by block 178, the input signal is converted to a temperature dependent signal having a desired temperature dependency. Referring to the functional block diagrams of the preferred embodiment of FIGS. 2 and 3, the temperature compensating circuits 78 and 11 of the respective figures.
8 operates to perform such steps.

Next, as shown in block 182, the temperature dependent signal is amplified by an exponential multiplier having a temperature dependence corresponding to and opposite to the temperature dependence of the temperature dependent signal, wherein: The resulting amplified signal forms a temperature independent signal that is exponentially related to the input signal. With respect to the preferred embodiment of FIGS. 2 and 3, such steps are performed by exponential multiplier circuits 86 and 160 of FIGS. 2 and 3, respectively.

In a preferred embodiment of the method of the present invention, the step of converting the input signal to a temperature dependent signal converts the input signal into a signal having a current level that varies according to the value of the input signal, as indicated by block 186. With steps.

FIG. 5 is a circuit diagram of the circuit 100, previously shown in functional block form in FIG. Voltage-current converter 108, temperature compensation circuit 1 shown in the functional block diagram of FIG.
18 and the exponential multiplication circuit 160 are indicated by the same numbered blocks, shown in dashed lines in FIG. Line 204 in FIG. 5 corresponds to line 104 in FIG.
Further, the input signal is supplied to the voltage-current converter 108.
Line 204 is coupled via resistor 208 to the negative input of amplifier 206. The DC voltage generated by voltage generator 210 is provided to the positive input of amplifier 206. A metal oxide semiconductor field effect transistor (MOSFET) 212 interconnects the output of amplifier 206 and its negative input. More specifically, and as shown, the gate electrode of MOSFET 212 is connected to amplifier 206
The source electrode of MOSFET 212 is connected to the amplifier 2
06 is connected to the negative input and the drain electrode of MOSFET 212 is connected to line 214. The signal generated on line 214 has a current level whose value varies in response to a variation in the value of the voltage level of the input signal provided on line 204. The line 214 in FIG. 5 corresponds to the line 114 in the functional block diagram in FIG.

In the preferred embodiment of FIG.
Consists of a pre-distortion / post-distortion amplifier and a bandgap current generator. The pre-distortion / post-distortion amplifier forms part of the temperature compensation circuit 118 and is a bipolar junction transistor 2
16,218,220 and 222. The collector electrode of each transistor 216-222 is connected to a respective one of the drain electrodes of MOSFETs 224, 226, 228 and 229. MOSFETs 224 and 226 are further connected together to form a current mirror. Similarly, MOSFET22
8 is coupled to MOSFET 230 to form a current mirror, and MOSFET 229 is coupled to MOSFET 231 to form a current mirror.

Voltage source 232 biases the base electrodes of transistors 218 and 220.

The emitter electrodes of transistors 216 and 218 are connected to line 23
Connected together by three. Line 233 is also connected to an amplifier circuit consisting of an amplifier 234.
In, the voltage generated by the voltage source 236 is supplied to its positive input. The emitter electrode of transistor 238 is connected to the negative input of amplifier 234. The emitter electrode of transistor 238 and the negative input of amplifier 234 are resistors
It is connected to ground via 240.

The emitter electrodes of transistors 220 and 222 are connected to line 24
Connected together by one. Line 241 is also connected to a bandgap current generator consisting of transistors 242, 244 and 246. MOSFETs 248 and 250 also form part of the bandgap current generator and are connected thereto in a current mirror configuration. Each MOSFET
The drain electrodes of 248 and 250 are connected to the collector electrodes of transistors 242 and 244, respectively. The emitter electrodes of transistors 244 and 246 are connected to ground via resistors 251 and 252, respectively. The drain electrode of transistor 230 is connected to the collector electrode of transistor 253, which forms a current mirror with transistor 254.

The ratio formed by the current levels on the pre-distortion / post-distortion amplifier lines 241 and 233 of the temperature compensation circuit 118 forms the gain of the amplifier. However, the current level on line 241 depends on the current level of the bandgap current generator due to the connection of line 241 to the collector electrode of transistor 246. Therefore, the final gain of the pre-distortion / post-distortion amplifier depends on the current level of the bandgap current generator. And since the bandgap current generator produces an output current at the collector electrode of transistor 246 that is temperature dependent, the gain of the pre-distortion / post-distortion amplifier is also temperature dependent.

The pre-distortion / post-distortion amplifier uses the current at the drain electrode of the MOSFET 231 and the transistor 254
An amplified signal, formed by the sum of the currents at the collector electrodes of the two, is generated in response to the application of an input signal provided thereto by line 214. Since the gain of the amplifier is temperature dependent, the amplified signal generated by the amplifier is temperature dependent. This signal is coupled to node 256,
It corresponds to the signal generated on line 156 in FIG.

The current at the collector electrode of transistor 220 is MOSFE
It is mirrored at the drain electrode of T230 and then at the collector electrode of transistor 254. Similarly, a current generated at the collector electrode of the transistor 222 is reflected on the drain electrode of the MOSFET 231.

Node 256 is also connected to the base electrode of bipolar junction transistor 264. Transistor 264 forms exponential multiplication circuit 160. Line 270 is connected to the collector electrode of transistor 264. The exponential multiplication circuit of the preferred embodiment of FIG. 5 further includes current sources 268 and 272, bipolar junction transistor 276, MOSFET 280, and resistor 284.
Is provided. Line 286 is current source 268 and transistor 276
Interconnect with the collector electrode of

Since transistor 264 comprises a bipolar junction transistor, the current generated at its collector electrode is governed by the exponential, temperature dependence previously described.
Similarly, the current generated at the collector electrode of the transistor 276 is governed by the same relationship.

 A mathematical description of the operation of circuit 160 is as follows.

The currents at the collector electrodes of transistors 276 and 264 are expressed as:

I _c276 = _Is276 exp [V _BE276 q / kT] I _c264 = _Is264 exp [V _BE264 q / kT] In this case, I _c276 is the current of the collector electrode of the transistor 276, and I _c264 is the collector electrode of the transistor 264. _S276 and _Is264 are the saturation current characteristics of transistors 276 and 264, and V _BE276 and V _BE264 are
And 264 are the base-emitter voltages, q is the electron charge, k is the Boltzmann constant, and T is the temperature of the bipolar junction transistor (scaled in absolute temperature).

If transistors 264 and 276 are similarly configured,
The saturation currents of the two transistors are essentially the same.

_Forming the ratio of the collector electrode current of transistor 264, I _c264 , to the collector electrode current of transistor 276, I _c276 , and by algebraic simplification, the following equation can be obtained:

I _c264 / I _c276 = exp [(V _BE264 −V _BE276 ) q / kT] In this case, V _BE264 −V _BE276 is simply the voltage drop of the resistor 284 or I ₂₅₆ × R ₂₈₄ , and R ₂₈₄ is the resistance 284 And I ₂₅₆ is the sum of the current at the drain electrode of the MOSFET 231 and the current at the collector electrode of the transistor 254.

 The substitution yields the following equation:

I _c264 / I _c276 = exp [I ₂₅₆ R ₂₈₄ q / kT] Since the current of the node 256, that is, I ₂₅₆ , is directly proportional to the temperature, T, the temperature dependency is canceled at the collector electrode and the transistor 264 The ratio of the collector electrode current and the transistor 274 collector electrode current does not change with temperature. Thus, the ratio formed from the current levels of the currents on lines 270 and 286 is the line 170 in FIG.
Corresponding to

The linear versus exponential circuit of the present invention, shown in FIG. 2 or FIG. 3 and FIG. 5, is an example of an automatic gain control circuit for a receiver, such as the receiver portion of a cellular radiotelephone in a cellular communication system. It can be suitably used to form a part. Because the linear vs. exponential circuit is independent of temperature, the gain control of the signal received by the radiotelephone does not change with changes in temperature.

In the United States, a portion of the 100 MHz frequency band extending between 800 MHz and 900 MHz is allocated for wireless telephony, such as cellular telecommunications. Traditionally, wireless telephones include circuitry that allows simultaneous generation and reception of modulated signals, thereby enabling two-way communication between the wireless telephone and a remotely located transceiver.

Referring now to FIG. 6, a cellular communication system is schematically illustrated. The cellular communication system is formed by placing a number of base stations at remote locations over a geographic area. In FIG. 6, the base stations are points 304,306,308,310,312,314.
And indicated by 316. Although FIG. 6 shows six separate base stations, it should, of course, be understood that an actual cellular communication system will traditionally consist of many base stations. Each base station 304-316 receives one or more modulated signals transmitted by the wireless telephone and includes circuitry for transmitting the modulated signal to one or more wireless telephones. Including. Each base station 304-316 is connected to a traditional wired, telephone network. Such a connection is indicated in the drawing by a dotted line, line 320
, Interconnecting the base station 316 and the wired network 324. Connections between the wired network 324 and the other of the base stations 304-314 can be shown as well.

Base station 30 forming a cellular communication system
Each position from 4 to 316 is carefully selected and at least one
One base station ensures that it receives a modulated signal transmitted by a radiotelephone located anywhere over the geographic area. In other words, at least one base station 306-316 must be within the transmission range of a radiotelephone located at any such location over the geographic area. (The maximum signal strength of the signal transmitted by the base station, and thus the maximum transmission range, is typically greater than the maximum signal strength of the signal generated by the wireless telephone, and the corresponding maximum transmission range, and therefore generated by the wireless telephone. The maximum transmission range of the transmitted signal is a major factor that must be considered when locating the base station in a cellular communication system.) Due to the spaced nature of the base station placement, the base stations 304-316 may The portion of the geographical area where it is located is associated with a respective one of the base stations. The portion of the geographical area proximate to each of the spaced base stations 304-316 defines a `` cell, '' which in the drawing is an area 304A, 306A, 308A, 310A, surrounding the respective base station 304-316. Represented by 312A, 314A and 316A. Cells 304A-316A together form the geographic area covered by the cellular communication system. A radiotelephone located within the boundaries of any cell of a cellular communication system may have at least one base station 30.
Transmit a signal modulated from 4 to 316 and said at least one
A modulated signal can be received from one of the base stations 304-316.

Referring now to the graphical representation of FIG. 7, a receiver transmitted by a transmission channel, such as a transmission channel defined as part of a frequency band allocated to wireless telephone communications, and such as a wireless telephone Are plotted as a function of frequency. The signal amplitude, scaled in volts on the vertical axis 350, is scaled by Hertz on the horizontal axis, and is graphed as a function of frequency. The energy of the received signal, represented by waveform 358 in the figure, is typically centered on the center frequency of a particular frequency, f _c , and is typically shown as a dotted line, here as shown. Symmetry around line 362.

The signal received by the receiver is kept within the desired range, and such a range is represented in FIG. 4 by the dotted lines 366 and 370. To keep the signal level within such a range, the receiver usually includes a gain control circuit. A gain control circuit amplifies the received signal if the signal level is too low, and attenuates the signal if the signal level is too high to keep the received signal within a desired range. I do. As mentioned earlier, since the gain control signal is typically scaled by dB / volt, the linear to exponential conversion circuit often forms part of the gain control circuit.

FIG. 8 shows a block diagram of the wireless telephone of the present invention, referenced generally by the reference numeral 400. Wireless phone 400 is the fifth
Includes the linear to exponential conversion circuit 200 shown. The signal transmitted to the wireless telephone is received by the antenna 404. Antenna 404 generates a signal on line 408 indicating the received signal. Line 408 is coupled to a filter circuit 412 that produces a filtered signal on line 416. The filtered signal generated on line 416 by filter 412 is provided as input to mixer circuit 420.
The mixer circuit 420 also has an oscillator 4
28 provides the oscillation frequency generated on line 424.

Mixer 420 is provided to filter 436 (often the first
A mixed signal is generated on line 432 (referred to as the downconverted signal of the Filter 436 is line 44
Generates a signal filtered out to zero, which signal is provided to an amplifier 441. Amplifier 441 generates an amplified signal on line 442, which is provided to mixer 444.

Mixer 444 further includes an oscillator 452 as an input thereto.
Receives the oscillation signal generated on line 448 by
As shown, oscillators 428 and 452 are connected to reference oscillator 464 by lines 456 and 460, respectively, to lock the frequency of oscillators 428 and 452 in a desired relationship with oscillator 464.

Mixer 444 generates a mixed signal (often referred to as a second downconverted signal) on line 486 that is provided to filter 472. Filter 472 generates a filtered signal on line 473 that is provided to amplifier 474. Amplifier 474 produces an amplified signal on line 482, which is provided to an analog-to-digital converter 486. A / D converter 486 is line 492
A signal is generated above, which is provided to a digital signal processor (DSP) 500.

The signal generated on line 482 is further coupled to an amplitude detector 520
The amplitude detector 520 detects the amplitude of the signal. Amplitude detector 520 generates a signal on line 530 which is provided to a linear to exponential converter 550, similar in construction to circuit 100 of FIG. Converter 550
Generates a temperature independent signal on line 560 that indicates the magnitude of the filtered signal generated on line 482. Line 560 is coupled to amplifier 474, which
4 changes the amplitude of the signal received on line 472 according to the value of the signal on line 560. This controls the gain of the receiver circuit of the radiotelephone 400.

Since the linear-to-exponential circuit 550 generates a temperature-independent signal, the DSP 500 (or demodulator 51
The change in amplitude of the signal generated by 0) is independent of temperature.

DSP 500 generates a signal on line 562, which is provided to a digital-to-analog converter (D / A) 564. D / A converter 564 generates a signal on line 566 that is provided to a converter, such as speaker 580. In some radiotelephones, the traditional demodulator, represented by the block 510 in the drawing and shown in dashed lines, is an A / D converter 486, DSP 500 and
Replaced by D / A converter 564.

The radiotelephone 400 of FIG. 8 further includes a transmitter portion with a transducer, such as a microphone 590.
590 generates on line 594 the signal supplied to modulator 598. Modulator 598 generates a modulated signal on line 602, which is provided to mixer 606. Mixer 606 is also provided as an input thereto with an oscillating signal generated on line 610 by oscillator 616.

Mixer 606 generates a mixed signal (often referred to as a first upconverted signal) on line 612, which is provided to filter 614. Filter 614 generates a filtered signal on line 618, which is provided to a second mixer circuit 622.
The second mixer circuit 622 also has as inputs to it:
An oscillator signal is provided by oscillator 630 on line 626. Oscillators 616 and 630 are
Similarly, oscillator 616 is coupled to reference oscillator 464 and
The oscillation frequency of the signal generated by 630 is maintained in a desired frequency relationship with the frequency of oscillator 464. Mixer 622 generates a mixed signal (often referred to as a second upconverted signal) on line 636, which is provided to filter 642. Filter 642 generates a filtered signal on line 648, which is coupled to antenna 404 to transmit the modulated and upconverted signal therefrom.

Since the logarithmic function is simply the inverse of the exponential function, by appropriately inverting the operation of the present invention, it is possible to generate a temperature independent signal that is logarithmically related to the input signal applied thereto.

For example, referring now to FIG.
The circuit of another embodiment of the present invention, shown at 900, is shown. Circuit 900 generates a temperature independent signal that is logarithmically related to the input signal.

The input signal formed on line 904 is a logarithmic multiplication circuit 908
Is applied to The logarithmic multiplying circuit 908 comprises at least one bipolar junction transistor and is operative to form a signal that is logarithmically related to an input signal applied thereto. Since the bipolar junction transistor forms part of the circuit 908, the log signal generated thereby is a temperature dependent signal.

A temperature dependent signal generated by circuit 908 is generated on line 916, which is coupled to temperature compensation circuit 922. Circuit 922 converts the logarithmic signal, dependent on the temperature applied thereto by line 916, to a temperature independent signal that is logarithmically related to the input signal. Circuit 922 responds to the temperature dependence of the logarithmic signal, which depends on the temperature applied thereto by line 916, and has a temperature dependence that is the inverse of the temperature dependence. Circuit 922 generates a temperature independent signal on line 928 that is logarithmically related to the input signal.

FIG. 10 is a block diagram of another embodiment of the present invention, referenced generally by the reference numeral 1000. Circuit 1000
Generates a temperature independent voltage signal that is logarithmically related to the input current signal.

The input current signal formed on line 1004 is a logarithmic multiplier
Applied to 1008. Logarithmic multiplier circuit 1008 comprises at least one bipolar junction transistor and is operative to form a signal that is logarithmically related to an input signal applied thereto. Since the bipolar junction transistor forms part of the circuit 1008, the log signal generated thereby is a temperature dependent signal.

A temperature-dependent signal formed by circuit 1008 occurs on line 1010, which is a voltage-to-current converter 1010.
Combined with 12. Voltage-to-current converter 1012 is line 10
10 converts the signal applied thereto to a current signal having a current level that varies according to the level of the signal applied to line 1010.

The current signal generated by converter 1012 is generated on line 1016 which is coupled to temperature compensation circuit 1022. Circuit 1022 converts the temperature dependent logarithmic signal applied thereto by line 1016 to a temperature independent signal that is logarithmically related to the input signal. Circuit 1022 corresponds to, and has a temperature dependence of, the temperature dependence of the logarithmic signal, which depends on the temperature applied thereto by line 1016.

Circuit 1022 generates a current signal on line 1028, which is applied to current-to-voltage converter 1034. Converter 1034 converts the signal applied thereto by line 1028 to a voltage signal having a voltage level that varies according to the current level of the current signal provided thereto by line 1028. Converter 1034 generates a voltage signal on line 1040 that is independent of temperature and that is logarithmically related to the input signal provided by line 1004.

FIG. 11 is a circuit diagram of circuit 1000, previously shown in functional block diagram form in FIG. The logarithmic multiplier 1008, voltage-to-current converter 1012, temperature compensation circuit 1022, and current-to-voltage converter 1034 shown in the functional block diagram of FIG. 10 are the same numbered blocks shown by dotted lines in FIG. Is displayed in.

Line 1104, coupled to the positive input of amplifier 1112,
This corresponds to the line 1004 in the figure. A diode 1114 is further coupled between the positive input of amplifier 1112 and ground.
The base electrode of transistor 1116 is coupled to the output of amplifier 1112, and the emitter electrode of transistor 1116 is coupled to ground via resistor 1118, and
Connected to 12 negative inputs.

Reference current generator 1122 is coupled to the positive input of amplifier 1126, and diode 1128 is connected between the positive input of amplifier 1126 and ground. The base electrode of transistor 1130 is connected to the output of amplifier 1126, and the emitter electrode of transistor 1130 is connected to ground via resistor 1132. The emitter electrode of transistor 1130 is further connected to the negative input of amplifier 1126.

The current generated at the collector electrode of transistor 1130 is MO
Reflected on line 1134 by the current mirror consisting of SFETs 1136 and 1138. Line 1134 is connected at one end to the drain electrode of transistor 1138 and at its second end to the collector electrode of transistor 1116. Line 1134 is line 1016 in the functional block diagram of FIG.
Corresponding to Line 1134 is connected to the base electrode of transistor 1144, the base electrode of transistor 1150, the collector electrode of transistor 1144, and the drain electrode of MOSFET 1152.

Like the temperature compensation circuit of FIG. 5, the temperature compensation circuit 1022 of FIG. 11 includes a pre-distortion / post-distortion amplifier and a band gap current generator.

Pre-distortion / post-distortion amplifiers are transistors 1144, 1146, 1148 and 1150, and MO
SFET 1152 and 1154, 1156 and 1158, 1160 and 1162
And a current mirror composed of bipolar junction transistors 1164 and 1166. Line 1167 connects the drain electrode of MOSFET 1162 to the collector electrode of transistor 1166. The base electrodes of transistors 1146 and 1148 are biased by voltage source 1168. The emitter electrodes of transistors 1148 and 1150 have their positive input biased by voltage source 1172 and their output coupled to transistor 1174.
Coupled to an amplifier circuit including 1170, the emitter electrode of the transistor 1174 is coupled to the negative input of the amplifier and to ground via a resistor 1176. Line 1177 connects the emitter electrodes of transistors 1148 and 1158 to the collector electrode of transistor 1174.

Bandgap current generators are bipolar junction transistors 1178, 1180 and 1182, and MOSFETs 1184 and 1
It consists of 186 current mirrors. The emitter electrodes of transistors 1180 and 1182 are connected to ground via resistors 1183 and 1184. Line 1188
Is connected at one end to the collector electrode of transistor 1182 and at its second end to the emitter electrodes of transistors 1144 and 1146. Similar to the temperature compensation circuit of FIG. 5, the ratio formed by the currents on lines 1177 and 1188 is the predistortion /
Form the gain of the post-distortion amplifier.

Current-to-voltage converter 1034 is formed from an amplifier 1190, whose positive input is connected to voltage source 1192 and whose negative input is coupled to line 1167. Resistor 1194 interconnects the negative input and output terminals of amplifier 1190. The signal generated on line 1196 is line 1104
Thereby forming a voltage signal that is logarithmically related to the input signal provided to diode 1112.

Although the present invention has been described with reference to the preferred embodiments illustrated in the various drawings, other similar embodiments can be used and have been described without departing from the present invention in order to achieve the same function as the present invention. It should be understood that modifications and additions can be made to the embodiments. Therefore,
The present invention should not be limited to any single embodiment, but rather should be understood in breadth and scope in accordance with the appended claims.

Claims (8)

(57) [Claims] 1. A circuit for generating a temperature independent signal that is exponentially related to an input signal, the circuit comprising at least one band operative to generate a current having a value proportional to temperature. A temperature compensated amplifier having a gap current generator, wherein the temperature compensated amplifier is coupled to receive the input signal and amplifies the input signal and thereby produces an amplified signal having a value proportional to temperature. And an exponential amplifier comprising at least one bipolar junction transistor having a base electrode, a collector electrode and an emitter electrode, the base electrode of said at least one bipolar junction transistor being generated by said temperature compensated amplifier. Coupled to receive the amplified signal at a value proportional to temperature, and The signal operates to bias the at least one bipolar junction transistor with a bias voltage having a value proportional to temperature, whereby the current generated at the collector electrode of the at least one bipolar junction transistor causes the current to be generated at the at least one bipolar junction transistor. The current exponentially related to the bias voltage of the base electrode of the junction transistor and thereby the current generated at the collector electrode of the at least one bipolar junction transistor depends on the temperature which is exponentially related to the input signal. A circuit for generating a temperature-independent signal that is exponentially related to the input signal. 2. The circuit of claim 1 wherein said amplified signal of a value proportional to temperature generated by said temperature compensated amplifier is directly proportional to temperature. 3. The temperature compensated amplifier according to claim 1, wherein said amplifier comprises a pre-distortion / post-distortion amplifier.
Circuit. 4. An exponential function converter for a gain control circuit of a wireless receiver for generating a temperature independent bias current exponentially related to a control voltage, said converter comprising: A voltage-current converter coupled to receive the control voltage to convert the control voltage into a current signal having a current, wherein the level of the current varies according to the value of the control voltage; A temperature compensated amplifier having at least one current source operable to generate a current, the temperature compensated amplifier being coupled to receive the current signal generated by the voltage-to-current converter and amplifying the current signal. And having a base electrode, a collector electrode and an emitter electrode, which operate to produce an amplified signal of a value proportional to temperature thereby. An exponential amplifier comprising at least one bipolar junction transistor, wherein a base electrode of the at least one bipolar junction transistor is coupled to receive the amplified signal at a value proportional to temperature generated by the temperature compensated amplifier. And the amplified signal operates to bias the at least one bipolar junction transistor with a bias voltage having a value proportional to temperature, whereby the current generated at the collector electrode of the at least one bipolar junction transistor is reduced. A current exponentially related to the bias voltage at the base electrode of the at least one bipolar junction transistor and thereby generated at the collector electrode of the at least one bipolar junction transistor is a factor in the input signal. To form a signal which does not depend on the temperature of functionally related, exponential converter comprises a. 5. The exponential function converter of claim 4, wherein said amplified signal of a value proportional to temperature generated by said temperature compensation amplifier is directly proportional to temperature. 6. The exponential function converter according to claim 4, wherein said temperature compensation amplifier comprises a current amplifier circuit. 7. The exponential converter of claim 4, wherein said temperature compensated amplifier comprises a pre-distortion / post-distortion amplifier and a bandgap current generator coupled thereto. 8. A circuit for generating a temperature-independent signal that is exponentially related to an input signal, the circuit comprising a current coupled to receive the input signal and having the input signal having a current. A voltage-current converter for converting the current into a signal, wherein the level of the current changes according to the value of the input signal; and at least one current source operable to generate a current having a value proportional to temperature. A temperature compensated amplifier having a temperature compensated amplifier coupled to receive the current signal generated by the voltage-to-current converter and amplifying the current signal and thereby an amplified value of a value proportional to temperature. And at least one bipolar junction transistor having a base electrode, a collector electrode, and an emitter electrode. An exponential amplifier, wherein a base electrode of the at least one bipolar junction transistor is coupled to receive a value of the amplified signal proportional to a temperature generated by the temperature compensated amplifier, and the amplified signal is Operative to bias the at least one bipolar junction transistor with a bias voltage having a value proportional to temperature;
The current thereby generated at the collector electrode of the at least one bipolar junction transistor is exponentially related to the bias voltage at the base electrode of the at least one bipolar junction transistor, and thereby the at least one bipolar junction transistor The current generated at the collector electrode of the input signal comprises a temperature independent signal exponentially related to the input signal; and to generate a temperature independent signal exponentially related to the input signal. Circuit.